New study shows antibiotic treatment does not reduce risk of secondary cardiac events

April 20, 2005

Taking antibiotics weekly for one year does not reduce the risk of a heart attack or other cardiac event for patients with stable coronary artery disease, according to a study funded by the National Heart, Lung, and Blood Institute of the National Institutes of Health. It is published in the April 21, 2005, edition of the New England Journal of Medicine.

Many previous studies have found the bacteria Chlamydia pneumoniae in the arterial plaque of patients with coronary artery disease. This led to the investigation of whether antibiotics could be used to treat the bacteria and therefore reduce the risk of cardiac events. Approximately 50 percent of U.S. adults have been exposed to C. pneumoniae at some point in their lives. It spreads through the air and can cause pneumonia.

"This study found no benefit from treating the C. pneumoniae bacteria with antibiotic in order to reduce the risk of heart attack or improve overall cardiac outcomes," said NHLBI Director Elizabeth G. Nabel, M.D. "We must continue to focus on the controllable risk factors for preventing coronary events."

ACES researchers randomly assigned 4,012 men and women to receive either once-weekly doses of azithromycin or placebo for one year. After an average follow-up of 3.9 years, there was no significant reduction of cardiac events, defined as death, heart attack, unstable angina, angioplasty or cardiac surgery, among participants receiving antibiotic compared to those given placebo. This lack of effect of antibiotic was shown for all participants regardless of age, gender, smoking status, or presence of C. pneumoniae antibody. The antibiotic treatment also had no affect on total mortality or on incidence of stroke.

Men and women were included in the study if they had stable coronary artery disease following a previous cardiac event such as a heart attack, angioplasty, or cardiac bypass surgery. Azithromycin was selected because of its proven effectiveness against the C. pneumoniae bacteria and for its once-weekly dosing.

ACES enrolled men and women at 28 centers across the country between 1999 and 2000. Pfizer, Inc., co-sponsored the study and supplied study medications.

"Although antibiotic treatment of patients with clinical coronary heart disease is not helpful, the ACES study was not designed to find the role of C. pneumoniae in the cause or progression of coronary heart disease. Different studies will be needed to determine the role of C. pneumoniae in the early, asymptomatic development of coronary heart disease," said J. Thomas Grayston, M.D, Professor of Epidemiology, University of Washington, Seattle, the study's principal investigator.

The ACES results are confirmed and extended by the similarly negative findings of the PROVE-IT trial published in the same issue of the New England Journal of Medicine. PROVE-IT tested a different antibiotic, a fluoroquinolone, and used a different treatment schedule with participants who were somewhat younger than those in ACES and who had an acute cardiac event at time of their enrollment in the study.
For more information or to schedule an interview, please call 301-496-4236 or email To reach J. Thomas Grayston, M.D., please call the University of Washington press office at 206-543-3620.

NHLBI is part of the National Institutes of Health (NIH), the Federal Government's primary agency for biomedical and behavioral research. NIH is a component of the U.S. Department of Health and Human Services. NHLBI press releases and other materials including information about heart disease, heart attack, and coronary artery disease are online at

NIH/National Heart, Lung and Blood Institute

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